Information codes such as two-dimensional codes have now been used in many applications. Such applications include an application in which a picture or a figure is arranged in the code area. For example, a technique provided by patent literature 1 is concerned with a two-dimensional code produced by strings of reverse-converted bits which are reversely converted from strings of bits. These strings of bits form a region of the code, in which the region is composed at a single gray level. The reverse-converted bit strings are converted based on information about a format for the two-dimensional code, thus producing a unique two-dimensional code with a design region composed of the single gray level.
In the technique shown by the foregoing patent literature 1, if the unique two-dimensional code has a design region composed of white modules, given design data are combined with the unique two-dimensional code such that a design composed of gray levels which can be read as white is formed in the design region. In contrast, if the unique two-dimensional code has a design region composed of black modules, given design data are combined with the unique two-dimensional code such that a design composed of gray levels which can be read as black is formed in the design region.